Having a crown or bridge affixed to a patient is achieved by basically a three stage process.
In the first stage, the dental surgeon removes the dead or cracked natural tooth. The surgeon then cuts down through the gingiva (i.e., the gum which held the tooth) to expose the underlying bone. The surgeon then burrs into the bone to insert a dental implant. The dental implant will act as the permanent anchor for the crown (which will be created during the third stage). The implant basically comprises a threaded bore to receive a retaining screw that is coupled at some portion to the crown. The crown is then secured to the dental implant by that retaining screw. The dental implant itself can be either press-fitted down into a hole drilled in the bone or it can be screwed down into that hole. The dental implant may have a male or female anti-rotational coupling (e.g., an external hex or internal hex, respectively) but in any case the entrance to the screw hole is located in the center of the anti-rotational coupling. A cover is then placed over the screw hole in the center of the anti-rotational coupling and the overlying gingiva tissue is then closed back over the implant. It is extremely important that sufficient time be allotted for osseointegration, i.e., the surrounding bone secures itself around the dental implant. This is achieved by allowing 3-4 months of healing time for dental implants in the lower jaw and 5-6 months of healing time for dental implants in the upper jaw.
Following this first stage healing, second stage healing begins. In particular, the surgeon cuts away the gingiva surrounding the head of the dental implant, removes the cover and then inserts a second stage healing cap which is releasably secured (e.g., screwed down) onto the head of the dental implant. A typical second stage healing cap is either cylindrical in form and/or circular in cross-section. In all cases, the healing cap is designed to maintain a cylindrical chamber, during second stage healing, from the gingiva crest (the top of the gum) down to the opening in the dental implant.
After approximately three weeks, the stitches are removed and the restorative doctor and dental technician then begin the third stage: creating a crown that is permanently secured to the dental implant. In particular, the healing cap is removed and a transfer impression is taken of the jaw containing the implant. The transfer impression basically is a mold that transfers the patient's dental information from the patient to a stone model. To preserve the location of the opening to the dental implant when creating the stone model, an impression post is coupled to the head of the implant. The impression post transfers the position information of the dental implant in the patient's mouth to the stone model. The impression post also prevents the transfer impression mold from entering into the opening to the dental implant.
When the transfer impression is completed and removed from the patient's mouth, the impression post is disengaged from the dental implant and reinserted into the hole preserved in the transfer impression. An implant analog is then attached to the impression post and the stone model is ready to be made.
The healing cap is then reinserted into the dental implant in the patient's mouth to continue to preserve the cavity in the gingiva until either the temporary and, eventually, the permanent crown is in place. A stone model is created from the transfer impression and the stone model becomes the model from which the restorative doctor and the dental technician create the crown/bridge. It is the model of the cavity, preserved in the stone model, that determines the final shape of the crown/bridge.
The following constitute various examples of United States patents disclosing healing cap systems.
For example, U.S. Pat. No. 5, 073,111 (Daftary) discloses a healing cap system in the form of a custom dental implant that is embedded in the jawbone and which can receive frusto-conical shaped healing caps and any one of three abutments that have different emergence profiles. Although this patent states that the healing caps are dimensionally similar to the tooth previously removed, the healing caps are all circular in cross-section and do not differentiate among the various possible tooth dimensions. Furthermore, the healing cap in this patent is coupled to the implant by being rotated so that the threaded surface of the healing cap is secured within the implant bore. Although the healing cap has a custom socket that fits over a raised lip on the implant head without damaging the lip during securement, use of this same healing cap with other conventional implants may damage the antirotational coupling on these types of implants. In addition, rotation of the healing cap to secure it to the implant may damage the surrounding gingiva tissue.
In U.S. Pat. No. 5,035,619 (Daftary), which is a continuation-in-part of the 5,073,111 patent, there is disclosed a two-piece (upper and lower) healing cap similar in design to the healing caps disclosed in the U.S. Pat. No. 5,073,111. The added feature of having an upper and lower portion of a healing cap permits the lower part of the healing cap (which engages the dental implant) to remain in place while the upper part is removed and the abutment (the stem which the crown will be formed upon in the third stage) is then coupled to the lower part of the healing cap, instead of having to attach the abutment directly to the implant. However, the deficiencies of the healing cap of the U.S. Pat. No. 5,073,111 remain in the healing caps of the U.S. Pat. No. 5,035,619.
U.S. Pat. No. 5,145,372 (Daftary) is also a continuation-in-part of the U.S. Pat. No. 5,073,111 and discloses a reinforced two-part healing cap. To that end, the lower part houses a threaded shaft rather than a threaded bore while the upper part houses a threaded bore. As in the U.S. Pat. No. 5,035,619, the upper part can be removed and an improved abutment, i.e., an abutment having a threaded bore, can be engaged to the lower part of the healing cap, instead of having to attach the abutment directly to the implant. However, as with the U.S. Pat. No. 5,035,619 healing cap, this improved two-part healing cap retains the same deficiencies of the healing caps of the U.S. Pat. No. 5,073,111.
In U.S. Pat. No. 5,246,370 (Coatoam) there are disclosed custom dental implants comprising an open upper portion which has the same general nonuniform shape of a removed tooth bone cavity. The implants have cylindrical prongs that are embedded into the patient's jawbone. The upper portion of the implant is shaped like the removed tooth and has matching inserts that fit within the upper portion. Each insert has a lower portion that is also shaped like the particular tooth removed (in order to seat within the upper portion of the implant) and a upper portion that is circular in cross section.
As an example of healing caps in the market, there is the Anatomic Abutments System.TM. sold by Dental Imaging Associates, Inc. of Sunrise, Florida which includes a cylindrical healing cap that is screwed down into the dental implant.
The problem with using a cylindrical healing cap is that a cylindrical cavity in the gingiva (which the typical healing cap creates during second stage surgery) does not imitate the dental anatomy of a tooth within the gingiva tissue. In other words, the actual periphery of the tooth that is in the gingiva tissue has a cross section that is not circular but rather has something similar to facets. Maintaining the facet structure within the gingiva is necessary to create a crown that has the proper emergence profile with respect to the gingiva. However, by using a cylindrical healing cap, the restorative doctor and dental technician must wax up the crown from a cylindrical opening in the gingiva (left by the cylindrical healing cap) which is not at all representative of the tooth that once resided there. It may be true that a cross section taken at one particular depth within the gingiva may happen to be circular but that is not true for the entire cross section of the tooth that resides in the gingiva.
As one skilled in the art can appreciate, the task of the restorative doctor and dental technician is difficult because the they are trying to create a crown from a somewhat flat gingiva surface, i.e., there is no natural tooth crater that guides them in molding a tooth. In addition, the crown and gingiva interface that the restorative doctor and dental technician are trying to create cannot easily replicate the tightly sealed interface that a natural tooth growing out of the gingiva would have.
Furthermore, once the dental implant is in place, the restorative doctor and dental technician have no room for adjusting the orientation of the tooth, i.e., the crown screw hole must be perfectly aligned with the vertical chamber left by the healing cap or else the crown will not be positioned correctly. Creating a crown which has a portion that must drastically taper to conform to the cylinder head of an implant is improper and thereby does permit the stimulation of soft tissue.
Moreover, where external hex implants are used (i.e., dental implants having a hexagonal-shaped anti-rotational coupling projecting upwards) the conventional cylindrical healing caps do not engage and seat over the hex but rather must be secured on top of the hex. In particular, on external hex implants the procedure to date is to select a separate spacing abutment to place over this particular type of implant that will allow the emergence procedure to begin at the gingival crest (the top surface of the gum). Because healing caps on these type of implants are also of a circular design, the height of the healing caps are frequently placed too high. The healing caps come in different millimeters of height. When the healing cap is above the height of gingival tissue the circumference of metal will show.
The result of all of this is that the restorative doctor and dental technician are trying to formulate a crown/bridge from criteria that are lost.
Therefore, a need exists for apparatus for creating and then maintaining the natural gingiva cavity throughout second stage healing that allows a restorative doctor and dental technician to easily and accurately create a close replica of the removed tooth that not only looks natural (i.e., being aligned with surrounding teeth and having proper tooth emergence profile from the gingiva) but also avoids soft tissue degeneration and destructive plaque build-up.
Furthermore, there is a need for a second stage healing cap that is compatible with a variety of standard dental implants and whereby the healing cap does not score or damage the anti-rotational coupling of the implant whenever the cap is engaged/disengaged from the implant.